1. Field of the Invention
The present invention relates a guiding system, a position controlling apparatus, and a guiding method. Particularly, the present invention relates to a guiding system, a position control apparatus, and a guiding method for guiding the position of a body-insertable apparatus in a subject.
2. Description of the Related Art
As examples of an apparatus for performing internal observation of a subject, such as a human or an animal, there are endoscopes that include tube-shaped probes (hereinafter, “endoscope”) and capsule-type endoscopes (hereinafter, “capsule endoscope”).
As examples of endoscopes, there are electric endoscopes that include charge coupled device (CCD) sensors and complementary metal oxide semiconductor (CMOS) sensors, which are provided on the tips of the endoscopes, and fiber scopes that include a bundle of optical fibers passed through a probe. The probe of such an endoscope is inserted from the mouth or the anus of a subject to take in-vivo images of the subject (see, Japanese Patent No. 3898781).
In contrast, a capsule endoscope is a capsule-type body insertable apparatus that is introduced into a subject, and it has a size swallowable by a human or an animal. The capsule endoscope is introduced into the subject from, for example, the mouth. The capsule endoscope that is introduced into the subject takes in-vivo images of the subject regularly, and transmits the in-vivo images of the subject as wireless signals to a receiving apparatus outside the subject (see, Japanese Patent Application Laid-open No. 2003-70728).
An observer individually or successively replays a plurality of images that are obtained by an endoscope or a capsule endoscope. By observing the images, the observer performs internal observation of the subject.
When a capsule endoscope is introduced into a subject, it is usually movable. Therefore, the position and the posture of the capsule endoscope in the subject are not restricted as long as they are not restricted by the inner wall of the lumen of the subject. However, if the position and the posture of the capsule endoscope in the subject are not determined, it is difficult for the observer to specify the part of the interior of the subject of which images are taken by the capsule endoscope. If the position and the posture of the capsule endoscope in the subject cannot be controlled, it is difficult for the observer to observe a target part of the interior of the subject.
To deal with the above inconvenience, a permanent magnet is mounted on a capsule endoscope. By applying an externally-formed magnetic field to the permanent magnet, the position and the posture of the capsule endoscope are controlled. For example, to control the position of a capsule endoscope that flows in liquid stored in the stomach of a subject, the magnetic field (hereinafter, “trapping magnetic field”) for maintaining the position and the posture of the permanent magnet is externally applied to the permanent magnet that is fixed in the capsule endoscope.
The difference in elevation of the intensity (hereinafter, “gradient”) of the trapping magnetic field is small near a target position where the capsule endoscope is to be held (hereinafter, “trapping position”). Thus, it is difficult to keep the capsule endoscope in a trapped state at a desirable position when the relative position between the subject and the capsule endoscope is changed. In other words, it is difficult to achieve a steep gradient of distribution of intensity of the trapping magnetic field near the trapping position to hold the capsule endoscope in the trapping position against a force, such as a frictional force or an inertia force, which is applied to the capsule endoscope.
For example, when the relative position between the subject and the capsule endoscope flowing in the liquid introduced into the subject is changed by moving a bed on which the subject is laid with respect to the trapping position, an inertia force and a frictional force of the liquid are applied to the capsule endoscope in the subject because the bed is moved. Accordingly, the capsule endoscope is to move with the subject. Because the gradient of the trapping magnetic field to prevent the capsule endoscope from moving is gentle near the trapping position, it is difficult to maintain the state where the capsule endoscope is trapped in a desirable position. The difficulty is similarly caused when the trapping position is moved while the subject is in a fixed state or when the bed and the trapping position are moved relatively.